Heretofore, in an air-conditioning apparatus such as a multi-air conditioning system for a building, refrigerant is circulated between an outdoor unit, which is a heat source device installed on the outside of the building, and indoor units installed inside the rooms of the building, for example. The refrigerant removes or gives off heat, and an air-conditioned space is cooled or heated using air that has been cooled or heated. A refrigerant such as a hydrofluorocarbon (HFC)-based refrigerant is often used as the refrigerant in such an air-conditioning apparatus. In addition, the use of natural refrigerants such as carbon dioxide (CO2) is also proposed.
Also, in an air-conditioning apparatus called a chiller, cooling energy or heating energy is generated in the heat source device installed on the outside of the building. Subsequently, a substance such as water or antifreeze is heated or cooled by a heat exchanger installed inside the outdoor unit, and the heated or cooled substance is then transported to an indoor unit such as a fan coil unit or panel heater to conduct cooling or heating (see Patent Literature 1, for example).
Also, there is a device called a waste heat absorption chiller in which four water pipes are connected between the heat source device and an indoor unit, and cooled and heated water or the like is supplied at the same time, thereby enabling cooling or heating to be freely selected at the indoor unit (see Patent Literature 2, for example).
Also, there is a configuration in which heat exchangers for a primary refrigerant and a secondary refrigerant are installed near each indoor unit, so that secondary refrigerant is transported to the indoor unit (see Patent Literature 3, for example).
Also, there is a configuration in which an outdoor device and a branching unit equipped with a heat exchanger are connected with two pipes, so that secondary refrigerant is transported to the indoor unit (see Patent Literature 4, for example).
Also, among air-conditioning apparatuss such as multi-air conditioning systems for a building, there exists an air-conditioning apparatus that circulates refrigerant from an outdoor unit to a relay unit, and circulates a heat medium such as water from the relay unit to indoor units, thereby reducing the transport power for a heat medium such as water while circulating the heat medium through indoor units (see Patent Literature 5, for example).